The invention relates to a method for operating vacuum installations under pressure changes between the operating pressure and the ambient pressure. The vacuum chamber of the vacuum installation has installed elements such as electronic components, transformers, motors, roller bearings and guide rollers provided with ventilatable coverings, i.e., coverings that can be ventilated. The guide rollers which are provided with roller bearings secured within the coverings on supporting bodies.
The change between the operating pressure, which most often is in the range of high-vacuum and specified by process conditions, and ambient pressure or atmospheric pressure occurs in particular when a substrate change, installing supplies of coating material, maintenance, repair or change-over is required. The pressure rise results from a process, also referred to as “flooding”, before a closure device of the vacuum chamber is opened. However, flooding, which occurs through an appropriately dimensioned flooding valve, causes dust or other particles accumulated in the vacuum chamber to be swirled up and suspended in the chamber. The term “flooding” as used herein means that the previously evacuated vacuum chamber is being refilled with a gaseous medium, preferably air.
As a rule, numerous installed elements such as electronic components, transformers, motors, roller bearings and guide rollers, are disposed in the vacuum chamber. These are provided with ventilatable coverings, for example with housings, capsules or the like.
The guide rollers or their segments themselves may form coverings for the roller bearings disposed therein Webs guided by the guide rollers, such as paper, metal and synthetic films also form a type of “covering”, which impedes and delays gas exchange.
As a rule the pressure rise in the coverings occurs, therefore, more slowly than in the relatively rapidly flooded vacuum chamber such that suspended particulates have a tendency to penetrate through openings, gaps, even through imperfect seals in the coverings, causing damage.
DE 27 25 331 C2 discloses lubricating the roller bearings of so-called expander rollers for a web transport within chambers with an oil mist pressure feed lubrication facility, two channels being disposed within the rollers curved in the form of an arc, for the inward and outward ducting of the oil mist, or the remaining air. However, the described method only operates properly if the expander roller is sealed with respect to the chamber, which is achieved either through an elastomeric sheathing of the rollers or by elastomeric adapters for rigid cylindrical roller segments. Flushing of the surroundings of the roller and the elimination of dust and other particles from the treatment process of the web is thereby not possible, especially not when during the flooding or, during the flooding of the installation with a flooding valve, dust and other particles are swirled up, which, while being in a state of suspension, have the tendency of penetrating into all nonsealed hollow spaces following the pressure rise due to the flooding.
DE 37 33 448 A1 discloses individually lubricating bilaterally sealed roller bearings of so-called expander rollers for a web transport through pressure lubrications with grease or oils, two channels being disposed within the roller curved in the form of an arc for the inward and outward ducting of the lubricants. However, adding air or another gas is not addressed, such that flushing the surroundings with gases is as little possible as is a gas flushing of the interior space of the roller or other components.
DE 39 19 425 C2 discloses periodically relubricating under control the grease charging of the individual roller bearings of curved, circumferentially closed expander rollers with base oil. However, mixing in air or another gas is not addressed, such that flushing of the surroundings with gases is not readily possible as is also not gas flushing of the interior space of the roller or other components.
The collective body of prior art dose not take into consideration the stirring up of dust or other particulate matter in a vacuum chamber during flooding with ambient air for the purpose of a web change under atmospheric pressure. The dust and other particles may have, for example, derived from a preceding coating process and which, due to the pressure rise during flooding, can penetrate into all coverings, housings or the like of the installed elements in the vacuum chamber and can significantly interfere with their function. This applies to the interior spaces of expander rollers with roller bearings as well as to the interior spaces of electric or electronic components. Especially hazardous is zinc dust, which is generated during the coating of films through the vaporization of zinc in the vacuum. Zinc condenses in the interior of the vacuum chamber on arbitrary surfaces and, together with the oxygen in the air, forms zinc oxide, and accumulation in roller bearings can lead to their wear-down.
In this connection it is especially necessary to take into consideration that, as a rule, expander rollers do not have a driving unit of their own but rather must be “dragged” by the film to be expanded. This has an especially negative effect with sensitive films in a thickness range of about 0.002 mm.
The goal of the invention is, therefore, to develop a method as described above so that all installed elements, enclosed in the vacuum chamber or installation and encompassed by an air-permeable covering or a housing, that covers or houses elements such as electronic components, transformers, motors, bearings and guide rollers which are protected against the penetration of suspended dust and other particles swirled up during the flooding from operating pressure (vacuum) to ambient pressure.
According to the invention this goal is attained in the above described method wherein before the vacuum chamber is flooded, a gas is introduced into the coverings so that the solid bodies such as dust and particles are blown out of the coverings e to prevent penetration of solid bodies into the covering.
The posed task is completely solved through these measures, i.e. all installed elements enclosed in the vacuum chamber or installation and encompassed by an air-permeable covering or a housing covering or housing elements such as electronic components, transformers, motors, bearings and guide rollers, are protected against the penetration of swirled up and suspended dust and other particles during the flooding from operating pressure (vacuum) to ambient pressure. The vacuum in the installed elements which, due to the gas throughflow, decreases more slowly, is a quasi cleaning means and a buffer against the penetration of foreign substances.
In the course of further implementations of the invention it is especially advantageous if, either singly or in combination the coverings are comprised of hollow rollers or roller segments, in which are located roller bearings with inner races and outer races and the gas is blown through the annular gap between the inner and the outer races, and/or if during the entire flooding process of the vacuum chamber the gas is ducted through said coverings.
In the following an embodiment example of the subject matter of the invention, its operational mechanism and its advantages will be explained in further detail in conjunction with FIGS. 1 and 2.